Stabilization of the knee joint (femur and tibia) is understood to be created primarily by four key ligaments: the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL) and the lateral collateral (LCL) ligament. The ACL is much better known, in part because injuries to the ACL are much more commonly diagnosed. The ACL keeps the tibia from sliding too far forward (anterior) with respect to the femur. Conversely, as depicted in FIG. 1, the PCL prevents the tibia from sliding too far backwards (posterior) with respect to the femur.
PCL tears are graded by severity (I, II or III) of the injury. The grade is classified by the degree of increased posterior tibia translation compared with that of the contralateral knee. In general, grading of the injury corresponds to the following:
Grade 1: The ligament is mildly damaged and has been slightly stretched, but is still able to help keep the knee joint stable. 1-5 mm.
Grade 2: The ligament stretches to the point where it becomes loose. This is often referred to as a partial tear of the ligament. 6-10 mm
Grade 3: This type of injury is most commonly referred to as a complete tear of the ligament. The ligament has been torn into two pieces, and the knee joint is unstable. 10 mm and greater.
As illustrated in FIG. 2, a PCL injury is typically sustained in a fall where the tibia is forced posteriorly regarding the femur. Another common way this injury occurs is when the knee hits the dash in a motor vehicle accident. PCL deficient knees may include significant knee pain and arthrosis in the medial and patellofemoral compartments. While the exact mechanism of articular degeneration in PCL-deficient knees is unknown, it has been found that PCL deficiency leads to significant increases of contact pressure in the medial and patellofemoral compartments, possibly leading to an increase in compartmental pressure due to increased anterior-posterior laxity and rotational instability of the knee.
PCL knee injuries often go surgically untreated, and a common form of treatment is to permit the PCL to heal on its own. When a PCL is torn, the proximal end of the tibia has a tendency to shift posteriorly which causes strain on the healing PCL, and results in a healed PCL longer than it was prior to injury. The healed knee may experience slack wherein the proximal end of the tibia shifts posteriorly after healing, causing a feeling of instability in the patient, and increasing the risk for further injury.
PCL injuries often are not isolated, and it has been found that concomitant posterolateral corner (PLC) injuries are common, particularly in a trauma setting. The PLC resists excessive varus and external rotation forces in the knee, and the PLC has a secondary role in resisting posterior translation of the tibia. When an injury of the PLC is combined with an injury of the PCL, the primary and secondary restraining effects of a tight PCL are lost at high knee-flexion angles. The PLC and PCL play a symbiotic role in resisting excessive external rotation and posterior translation of the proximal tibia.
The natural history of chronic PLC injuries includes varus thrust gait, posterolateral instability, and developing arthrosis. Similar to PCL-deficient knees, developing arthrosis in PLC-deficient knees is likely due to altered knee kinematics and increased peek compartment pressures.
An orthopedic device, such as a knee brace that provides support to the back of the upper calf throughout the range of motion, may be used to prevent this unwanted shifting. In the post-operative patient (or even the recently injured patient, who has not had, or will have, surgery), this may mitigate the lengthening of the PCL during healing, and prevent the shifting problems described above. In the patient having a PCL that has healed in a lengthened state, the brace may prevent the undesirable shifting described above, giving the patient an added feeling of stability, and a decreasing risk of further injury.
Unfortunately due to poor diagnostic methods, there is uncertainty as to the annual volume of PCL tears (estimated between 3% and 20% of all ligament injuries). PCL injuries have historically been considered to have benign clinical consequence. Thus if the PCL tear had been diagnosed, it would often go untreated since it resides outside the joint capsule and has the ability to heal itself. Unfortunately, when left to heal on its own, the PCL typically heals in an elongated length, resulting in joint instability.
Recent estimates place the number of diagnosed PCL tears in the US near 25,000 annually. When compared to the number of ACL tears, it places the percentage at roughly 10%. The question still remains as to how many knees go undiagnosed. The problem is that if an effort is not made to repair the ligament to maintain its normal length, it will heal in a stretched position, creating excessive movement between femoral and tibial joint surfaces; this raises the likelihood of degenerative changes in the knee leading to osteoarthritis.
PCL reconstruction has been recommended by some clinicians for more severe injuries, or for PCL injuries combined with other types of injuries. Even though some in-vitro biomechanical studies have reported that PCL reconstruction can restore knee biomechanics in a model with an isolated injury, the actual surgical management of PCL injuries has been problematic; a high number of patients continue to experience residual knee laxity after surgery.
Loads on the PCL have been shown to be dynamic in nature. As the knee is moved for instance, from a position of full extension to 90° of flexion, the tension on the normal intact PCL ligament increases. This increased tension helps to keep the tibia properly positioned with respect to the femur. When the PCL is damaged, it is not able to provide this increased tension and may allow the tibia to shift posteriorly. As mentioned above, if a brace could apply an external force to the posterior calf and in proper measure, it would provide the forces necessary to effectively co-locate the femur and tibia. It has been found that one possible cause for poor patient outcomes in treatment of the acute PCL injury is that the dynamic loads pull the tibia posteriorly during the healing process, and cause the PCL to heal in an elongated length. This may also result in an increased incidence of future osteoarthritis.
A properly designed dynamic brace could prevent or mitigate this occurrence. If surgery is required, this brace could offer protection for the reconstructed PCL throughout its healing process. Since the PCL is extracapsular and has the ability to heal on its own, such a brace may potentially prevent the need for surgical management. For the patient who has had a previous PCL injury and experiences joint laxity as no subsequent surgical intervention was undertaken, this brace may also provide enhanced stability and confidence. Ultimately, such an orthopedic device could benefit patients with all levels of PCL injuries. Another cause of poor outcomes is due to the gravity effect. As the patient lays supine and lifts the leg with the knee extended, the tibia falls posteriorly. This effect can be a regular occurrence while the patient is in the non weight bearing post operative phase where they can regularly experience this posterior shifting of the tibia simply by laying in bed.
The posterior shift of the tibia can be detrimental to the healing PCL and cause undue tension leading to a non-anatomical lengthening of the ligament. There are many PCL brace options available, however the known solutions lack certain critical functional requirements. Most options are static braces that only provide a constant anterior force through the entire arc of knee motion. While these static braces are capable of providing some stability to PCL-deficient knees, they do not adjust the stability in high degrees of knee flexion. Tension within the PCL varies through the knee arc motion.
Therefore, it is proposed herein to provide an orthopedic device in an exemplary form of a PCL brace that meets the certain critical functional requirements to effectively treat a PCL injury of the knee, and concomitant other injuries of the knee such as the PLC and patellofemoral pain. The proposed device will be to help support the functional healing of an acute PCL injury post operatively or non-operatively. Another purpose is to maintain the proper bone alignment of the femur and tibia for the patient with poorly healed/elongated PCL. Thus, the proposed device would be appropriate for all new PCL injuries and all those patients who never received surgery to preserve PCL length.